Methods to Produce Stretchable Products

ABSTRACT

The invention provides methods for producing flexible, stretchable, and/or elastic products comprised principally of material such as natural elastomers and other synthetic polymers. The method for producing stretchable products by spraying product material over a workpiece former, and method for creating perforated products by spraying product material over fibres in an upright position. The invention provides methods for making double sided fibre coating of the product and, or to at least coating the product surface on the side facing the wall without the need for removing the product from the wall.

CROSS-REFERENCE

This application is a continuation-in-part of U.S. nonprovisionalapplication Ser. No. 11/268,684 filed Nov. 7, 2005, which claims thebenefit of U.S. provisional application Ser. No. 60/625,480 filed Nov.5, 2004, the disclosures of which are incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

The present invention relates to methods for producing products such astwo-dimensional and three-dimensional products, composed of flexible,stretchable and/or elastic materials such as natural elastomers andother synthetic polymers. The invention also relates to methods forcoating the products with fibres, making perforated stretchableand/elastic products.

BACKGROUND OF THE INVENTION

Methods for making products of natural or artificial latex rubbers areknown in the prior art, however the resulting products are merelynon-breathable and their feel on the body is rubbery. When loose fibresare applied prior to the application of the product material to create acomfortable tactile feel, the fibres are soaked by the product materialmaking it hard to obtain a even velvet inner fibre coating. Accordingly,there remains a need for an improved methods for producing breathablestretchable products with a desirable tactile feel.

SUMMARY OF THE INVENTION

The present invention is generally related to methods for producingstretchable, elastic or shape-retaining products composed principally ofmaterials such as resilient elastomers including but not limited tonatural latex rubber or polyurethane, using controlled spraying of theprincipal material onto a surface of a wall such as a workpiece former.The resulting product may have a uniform thickness or differentthicknesses at different regions as desired. The present invention isalso directed to improved methods for preparing products having a singleor double-sided surface coating of loose fibers, and a method forgenerating microporosity in such products.

In one embodiment of the invention, a method is provided for producing astretchable workpiece, said method comprising the steps of: (a) applyinga wetting agent onto a surface of a wall; (b) applying a first layer ofloose fibres onto at least a portion of the surface of the wall toproduce at a partially fibre-coated surface; and (c) spraying a liquidproduct material onto the fibre-coated surface to form a productmaterial layer of predetermined thickness on the fibre-coated surfaceand produce a stretchable workpiece, wherein the product material layerhas an inner and outer surface and the fibres are attached to the innersurface of the product material layer.

In one aspect of this embodiment, the method further comprises the stepof applying a second layer of loose fibres onto the outer surface of theproduct material layer. The loose fibres may be applied directly to theouter surface of the product material layer where the product materiallayer is wet or has not fully dried. Alternatively, the product materiallayer may be dried first and then at least one layer of an adhesive or asecond product material layer is applied to the product material layerto form an adhesion layer. The loose fibers may then be applied to theadhesion layer. This allows for the formation of products having innerand outer surfaces coated with loose fibres.

In another aspect of this embodiment, the method further comprises thesteps of: allowing the product material layer to dry;

In another embodiment, the invention provides a method for producing astretchable workpiece, said method comprising the steps of: (a) coatinga surface of a wall with a gel; (b) applying a first layer of loosefibres onto at least a portion of the surface of the gel coated wall, ina manner that the loose fibres are anchored in said gel and held by thegel at substantially upright position relative to the wall surface (e.gby electrostatic flocking technology) the fibres partially covered bythe gel; to produce at least a partially fibre-coated surface; and (c)spraying a liquid product material onto the said substantially uprightstanding fibres in a manner that the fibres are embedded in the productmaterial droplets network, to form a product material layer on thefibre-coated surface and produce a stretchable workpiece, wherein theproduct material layer has an inner and outer surface and the fibres areattached to the inner surface of the product material layer at asubstantially upright position.

These and other embodiments of the invention will become apparent inlight of the detailed description below.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a representative workpiece. In 1A, the workpiece is on aformer wherein the first layer of fibres is applied into the wettingagent. In 1B, the workpiece has been displaced from the former and thewetting agent has been removed.

FIG. 2 represents a surface view of the workpiece showing amicro-perforated layer created by the spray droplets.

FIG. 3 represents a section of the workpiece showing micropores formedby the network of droplets.

FIG. 4 represents a representative process for preparing a finishedworkpiece which entails (A) applying an aqueous solution to a former;(B) applying fibres onto the aqueous solution on the former; (C)applying product material over the embedded fibres; and (D) applyingfibres on top of the product material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally related to methods for producingstretchable, elastic or shape-retaining products composed of principalmaterials comprising resilient elastomers such as natural latex rubber,polyurethane or other synthetic materials, in a spray able liquid state,using a precise controlled spraying of the liquid material onto asurface of a wall such as a workpiece former. The resulting product mayhave a uniform thickness or different thicknesses at different regionsas desired. The present invention is also directed to methods forpreparing products having a flocked single or double-sided surface, thatis a surface coated with loose fibers, and methods for generatingdesired porosity in order to gain breathability of such products. Thepresent invention is also directed to products produced by the inventivemethods, a workpiece former, and apparatus for preparing products basedon product material spraying. The product produced by the invention hasan improved cozy feeling on both sides of the product. A textile-likefeeling and a ‘textile movement noise’ is achieved by using the methodsand former of the invention.

The term “flock” or “flocking” refers to the process of applying,attaching, or adhering loose fibres onto a surface.

The terms “former,” “mould,” or “workpiece former” are usedinterchangeably. A former or mould is an object made of any desiredshape or size and serves as shape former for the making of products. Forexample, if a product in the shape of a face mask is desired, then aformer or mould may be constructed that displays the shape and size ofdesired face mask. The former may be flat and two-dimensional such as aflat belt conveyor. Alternatively, the former may be three-dimensionaland have a complex shape to which a workpiece substantially conforms. Inaddition, the former may be made of any suitable material such as metal(e.g., aluminium), porcelain, ceramic, plastics, or composite (e.g.,metal and plastic).

The terms “product” and “workpiece” are used interchangeably and mayalso include any object that can be produced using the methods,apparatus, and formers of the invention. Stretchable, elastic productshave a variety of uses including, without limitation, industrial usesuch as pipes, seals, membranes sheets, filtering membranes; foodindustry such as breathable stretchable wrappers or coverings forobjects including perishables such as food; medical industry for medicalproducts such as dressings and bandages; sanitation, athletic, andpersonal hygiene industries such as garments including protectivegarments and undergarments like brassieres, undershorts, socks, orgloves and any other garment, undergarment or dressing for veterinary oroutdoor use. Other examples of garments are described in U.S. Ser. No.10/723244, filed Nov. 26, 2003, and in U.S. Ser. No. 09/744,779, filedAug. 5, 1999, both of which are incorporated by reference in theirentirety.

The phrase “loose fibres” refers to any suitable loose flocking fibrematerial including natural or synthetic materials and may behydrophilic, hydrophobic, or a combination of the two. Hydrophilicfibers include wettable fibers, i.e., hydrophobic fibers that have beentreated. with to render them hydrophilic, absorbent fibers, andsuperabsorbent polymer fibers. Examples of wettable fibers includebicomponent fibers, polypropylene fibers, and polyester fibers that havebeen treated for example with surfactants. Example of wettable fibersare polyester fibers, such as DuPont-Akra Polyester Type 11A Brightcommercially available from DuPont Company treated with a surfactantsuch as Tween 20 commercially available from ICI Americas Inc. Absorbentfibers are hydrophilic fibers. Absorbent fibers may comprise rayonfibers, acrylic fibers, nylon fibers, polyvinyl alcohol fibers, andfibers of natural or regenerated cellulosics. Example of absorbent fiberis rayon fibers. Superabsorbent polymer fibers are hydrophilic fibersthat are swellable and capable of absorbing greater than about 5 gramsper gram (of fiber weight) of 1% saline solution. Examples ofsuperabsorbent polymer fibers are polyacrylate fibers, fibers of graftedcellulose, and fibers of maleic acid. Examples of superabsorbent polymerfibers include OASIS Type 101, commercially available from TechnicalAbsorbents Limited and CAMELOT, commercially available from Camelot,Alberta, Canada. A preferred fibre for use in the invention is cottonfibres. Any suitable method for delivering the loose fibres so that theymay be applied to the surface can be used. For instance, the loosefibres can be sprayed or blown onto the surface of the wall as well aselectrostatically and or pneumatically flocked.

The phrase “product material” comprises suitable stretchable materialsuch as natural or synthetic polymers. A natural polymer includes,without limitation, latex rubber. A synthetic polymer includes, withoutlimitation, polyurethane. For spraying purposes, emulsions, suspensions,or solutions of the product material, e.g., liquid latex rubber, aregenerally used. After spraying the product material, with or withoutadditional process steps, the product material is preferably allowed todry before it is removed from a surface. The drying process may includecuring or setting processes, depending on the choice of productmaterial. For example, when latex rubber is used as the productmaterial, the latex rubber would cure as it dries. In practicing thisinvention, the preferred product material is natural latex rubber whichforms durable, flexible, stretchable, elastic shape-retaining products.

The term “wall” may refer to a flat or two-dimensional work piece formersuch as a flat conveyor belt or any suitable shaped flat surface towhich a product substantially conforms. Alternatively, the wall may be athree-dimensional workpiece former having a complex shape to which aworkpiece substantially conforms. Alternatively the wall may be nonflat, embossed or complex shaped conveyor belt, perforated conveyorbelt, or combination thereof. The wall may be made of any suitablematerials such as plastic, rubber, composite ((e.g. of metal and plasticor ceramic), ceramics, metal such as aluminum or stainless steel.

Prior to the present invention, the manufacture of products havingdouble flocked surfaces is not easy thing to do. Typically, the outersurface of a product contained on a mould would be initially flocked. Toflock the inner surface of the product, the product is generallystripped off the mould and turned inside out so as to expose theunflocked inner surface. Adhesive material is layered onto the unflockedinner surface, then loose fibres are applied to the adhesive layer.Because of additional mechanical removal and adhesive application steps,the process of producing double sided flocked products can be difficultand expensive, particularly when thin products are involved. The presentinvention provides a surprising and significant improvement of thedouble sided fibre coating procedures by reducing the number of processsteps and entailed costs. Moreover, the present invention provides asurprisingly effective and economical way to produce thin products thatare flocked at their inner and outer surfaces.

Thus, the inner surface flocked product can be used to prepare a doublesided flocked product and in another embodiment of the invention, themethod further comprises the step of applying a second layer of loosefibres onto the outer surface of the product material layer. This allowsfor the formation of products having double-sided flocked (inner andouter) product material surfaces without the need of mechanical removalof the initially flocked product from the former.

As discussed above, the loose fibres may be applied to the surface ofthe wall by any suitable means. To allow the loose fibres to temporarilyadhere to the surface of the wall prior to applying the product materiallayer, the surface may be wetted with a suitable medium or wetting agentprior to the application of the loose fibres. Representative wettingagent include an aqueous medium such as water, an aqueous solution(e.g., surfactant solution), or a suspension, (e.g. a gel such as ahydrogel) and a surfactant solution, The wetting agent should notinterfere with the flocking procedure or cause any degradation of theproduct material layer. Upon product material spraying, the loose fibreswill stick to the product material layer and result in the generation ofan inner flocked layer on sprayed product. The solvent in the wettingagent will dry or evaporate anyway during the drying or curing step ofthe main product layer, leaving little or no residue. The residue wouldnot interfere with the characteristics of the product such as softtactile feel. If desired, however, the residue may be removed by anysuitable means such as washing or soaking the product in an aqueoussolution, e.g., water, to remove or leach out any residue.

In some embodiments of the invention, the wetting agent comprise asolution having less than 5 weight percent of cellulose. In anotherembodiment, the wetting agent is a gel having more than 95 weightpercent of liquid and a small amount of a gelatin base substance, forexample gelatin, surfactant, or cellulose. The wetting agent does notreact or stain the liquid product material, and can be easily removedfrom the finished workpiece. The wetting agents of the invention shouldhave such viscosity which holds the fibres in a stable position. Forexample, the wetting agent may comprise glycerin, hydroxyethylcellulose, propylene glycol, synthetic or natural polymers, proteins,carbohydrade, sorbitol, polysorbat, acrylamide, methacrylamide,N-alkylene methacrylamide, N-dialkyleneamino-alkylene methacrylamide,N-dialkyleneamino-alkylene methacrylamide, N-methylol-methacrylamide,N-vinylformamide, N-vinyl-acetamide, N-vinyl-N-methyl-acetamide,N-vinyl-N-methyl-formamide, hydroxy-ethyl-acrylate, methacrylicacid-ester of polyethylene-glycol-mono-allyl-ether, or allyl ether ofpolyethylene-glycol. For example, the wetting agent which can be used inthe invention are hydrogels (Hydromer, Inc., Cambridge Polymer Group,and Vitality Medical).

In one embodiment of the invention, a method is provided for producing astretchable workpiece, said method comprising the steps of: (a) applyinga wetting agent onto a surface of a wall; (b) applying a first layer ofloose fibres onto at least a portion of the surface of the wall toproduce at a partially fibre-coated surface. The loose fibres areflocked electrostatically or by any other suitable way so that they hitthe wall substantially perpendicular to its surface; and (c) spraying aliquid product material onto the upright standing fibres to form aproduct material layer of predetermined thickness on the fibre-coatedsurface and produce a stretchable workpiece, wherein the productmaterial layer has an inner and outer surface and the fibres areattached to the inner surface of the product material layer. Anotherembodiment further comprising the step of applying a second layer ofloose fibres onto the outer surface of the product material layer,wherein the product material layer is uncured or partially uncured. Inanother embodiment, the method further comprising the steps of: allowingthe product material layer to dry; and removing the stretchableworkpiece from the surface. After the workpiece is removed from thesurface, the gel can be evaporated so that little gel residue remains onthe first layer of fibres. The residue can be subsequently removed orreduced by washing of the product with an aqueous medium, e.g., water.

In one embodiment, the product material layer has different thicknessesat different areas, or the same thickness at different areas. The wallis flat, such as a flat conveyor belt, or the wall is a workpieceformer. In another embodiment, the workpiece former comprises a complexshape to which the workpiece substantially conforms. In still anotherembodiment, the wall comprises a plurality of perforations, and thespraying is carried out such that at least no substantial productmaterial layer forms over the perforations.

In one other embodiment, the fibres are made of natural or syntheticmaterials, for example, lightweight cotton fibres or viscose fibres or acombination of the two. In another embodiment, the liquid productmaterial comprises a natural or artificial elastomer. A naturalelastomer can comprise natural latex rubber, and an artificial elastomercan comprises polyurethane.

In one embodiment of the invention, step (a) comprises applying thewetting agent at a predetermined thickness and viscosity range. In apreferred embodiment, the wetting agent is at a viscosity of about 300to about 10,000 cps. In another preferred embodiment, the wetting agentis a gel, or a solution comprising less than 5 weight percent ofcellulose.

In another embodiment of the invention, step (b) comprises applying thefibres so that fibres penetrate the gel perpendicular to the surface ofthe wall and the gel holds the fibres in an upright position. In stillanother embodiment, step (c) comprises spraying the liquid productmaterial on top of the upright fibres to create a web of the sprayedliquid product material on top of the upright fibres. The intensity anddrop size of the sprayed liquid product material can be controlled sothat the sprayed liquid product material forms a porous layer or aunified and even layer. In one embodiment, the layer is micro-porous.

In some embodiments, the flocking of the fibres onto the wetting agentin the form of a gel foundation is preferably done electrostatically sothat the strong movement of the fibres towards the wetted former causesthe fibres to move and penetrate the gel at a perpendicular to theformer surface, because of the air resistance effect. The fibres willpenetrate the gel layer which will hold the fibres upright and willcover a part of each fibre, the part of the fibre that penetrated intothe gel.

Spraying liquid product material, such as latex, on top of the uprightfibres results in a web-like layer of the sprayed polymer on top of theuncovered, upper side of the upright fibres. Formation of such web-likelayer can be efficiently carried out by controlling the intensity of thespray which in turn controls the continuity of the sprayed layer createdby the spraying the product material. Such a procedure creates a porouslayer, or a micro-porous layer, or a more unified and even layer. Thecontrol of spray intensity, droplet size and surface tension of theproduct material enables controlling the finished product porosity andbreathability.

Control of spray intensity can be done for instance by controlling thespray gun movement speed relative to the wall surface, droplet size canbe controlled by changing the atomizing air pressure and sprayedmaterial pressure changing the nozzle orifice diameter and changing thespraying liquid viscosity. The surface tension can be controlled bychanging the chemical formulation, properties and dilution of theproduct liquid material The micro-porous or micro-perforated layer iscreated when droplet size is relatively big and when surface tension isrelatively high so that drops do not easily join together, leaving smallspaces between them. The small amount of liquid absorbed by the fibresimmediately after spraying the product material over the fibres isanother reason for the creation of an uneven micro-porous layer.

In one embodiment the creation of the product layer is done in severalspraying steps, so that the uneven poroused product material layer isfirst cured or partly cured, then a second layer is sprayed, in that waysurface tension effect of the second layer keeps most of dropletsjoining the web previously created, enabling the creation of thicker andstronger layer while keeping the microporosity of the work piece.

The wetting agent is preferably aqueous solution that can be applied tothe surface of the wall to hold the fibres onto the surface of the wall.In some embodiments, the wetting agent is viscous, for example, havingthe viscosity of honey or that of a gel material. For example, theviscosity of the wetting agent can be in the region of about 300 toabout 10,000 CPS.

The workpiece so formed from the methods comprising a wetting agent thathold the fibres upright on the surface of the former exhibit manysurprising and unexpected results that provides a workpiece of superiorproperties. Use of a thick wetting agent together with the electrostaticflocking technique followed by the controlled droplets spray of theproduct material layer, has the advantage that the fibres are held in asubstantially upright position to produce workpiece surfaces that areuniformly and efficiently coated with fibres on the inner side of thelayer, without the fibres being soaked by the product material layer.Since the perpendicular standing fibers penetrated the wetting agent,they are held in the perpendicular position by the wetting agent and arepartly covered by the said wetting agent temporary.

When sprayed product material liquid is applied on top of the fibres,the covered part of the fibres is protected from being coated by thesaid product material liquid, at this stage change of roll is takingplace, the product material liquid is taking the roll of keeping thefibres in place, still perpendicular to the surface. At a latter stage,the wetting agent will be washed out or evaporated, reviling thepreviously covered part of the fibres, which will be now standing freeout of the product material layer substantially perpendicular to itssurface. This create a smooth and velvet fiber layer that is coating theinner surface of the product layer in a similar way to the externalflocked surface, a result that cannot be achieved in any other way.

Further, the upright fibres of the inner layer promote the formation ofa breathable workpiece because the upright fibres enhance the formationof pores in the workpiece.

In further another aspect of this embodiment the wall surface is a flatsurface.

It will be appreciated by persons skilled in the art of that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes variations and modification of the various features describedin the specification and shown in the drawings which may occur to aperson of ordinary skill in the art upon reading the foregoingdescription and which are not in the prior art.

1-29. (canceled)
 30. A stretchable workpiece comprising: (a) a porous or micro-porous webbed layer of partially connected droplets of a resilient elastomeric material, the layer having an inner and outer surface; and (b) loose fibers partially embedded at least in one surface of the layer.
 31. The workpiece according to claim 30, further comprises loose fibers partially embedded in the inner and outer surfaces.
 32. The workpiece according to claim 30 or 31, wherein the fibers are made of natural or synthetic material.
 33. The workpiece according to claim 30, wherein the resilient elastomeric material comprises a natural or synthetic material.
 34. The workpiece according to claim 33, wherein the natural material is latex rubber.
 35. The workpiece according to claim 30 or 31, wherein the layer has uniform thickness or different thicknesses at different areas.
 36. The workpiece according to claim 30 or 31, wherein the webbed layer is perforated. 